I think Eloise and Widmore are aligned with this Man in Black--that's why she was adamant that they bring Locke's corpse with them on the plane.
I wondered about Ben's casually and sardonically revealing to John that he was a Pisces--then I remembered Jacob with the fish (a red herring, no less) at the beginning of the episode. Gutting a fish and throwing it on the fire/being gutted by a man under the sign of the fish and thrown on a fire...everything's connected.

Add this to the never ending theories about Lost, but I have one for this. I think Jacob has visited everyone who has ever come to the island (Well, maybe not everyone, but the significant ones and then they probably brought some insignificant people along with them). When the man in black asks Jacob who were the people in the ship they saw off the coast and how they found the island, he answered himself saying it was Jacob who brought them here. Then he talks about how they'll do the same as everyone, come, fight, corrupt, destroy. Jacob declares this as progress and that it only "ends" once.
What I think is happening here is that Jacob has brought all these people to the island, the black rock, the Dharma Initiative, Desmond, other possibly castaways and most importantly the Oceanic flight 815 survivors. He brings them to the island by visiting them at very significant points of their lives, and influencing there fate to come to the island. The only difference with the Oceanic 815 guys is that everyone before them that he has brought to the island was progress, but these castaways are going the lead the "end" that he talks about.
I am also thinking that Not!Locke is like Ghost Christian. The real Locke and Christian are dead, but Not!Locke and Ghost Christian are manifestations of the island. However, Ghost Christian speaks on behalf of Jacob and I think Not!Locke speaks or acts on behalf of the evil part of the island. Whoever the man in black was, he got to possess Locke, while Jacob got Christian.
Christian was "the man in black" / Not!Locke . He is the one who told Locke he had to die and took Charlotte away.
He was appearing as Christian to set his plans in motion

No. House's detox and sex with Cuddy were a hallucination. Everything that happened this episode was real, except that the lipstick was actually a pill bottle. When Cuddy came into his office in the morning, she wasn't talking about the sex that didn't happen, she was talking about him crossing a line with his comment about her baby. House did tell Wilson about having sex with Cuddy and Wilson believed him, but it never actually happened.

In the beginning, when Jacob was talking to the "dark dude", it was implied that Jacob was bringing that ship to the island. Why? Did they both need new souls or bodies or something to live forever? Do we think that one of them is the physical manifestation of that Egyptian god?
Just hard to wrap my mind around Jacob visiting all of our main losties at some point during their lives. If he knew, did he want to die? He certainly didn't seem to say anything to Ben to make him stop, when he very easily could have. It seemed that Jacob made a point to touch everyone he visited (I think--I'm blanking on whether or not he touched Sayid). I wonder if that's significant?
So who is Alana and her buddies? Clearly she knew Jacob, was she a former other or some sort? A descendant of others? Man they have a lot of questions to answer next season.
Is anyone else SUPER ANNOYED by the Locke plot twist?? I've invested five years of my life in this damn show, thinking Locke was special. But he only thinks he's special because Richard told him because Locke told HIM. We finally see him take hold of his "destiny" and it turns out it's NotLocke, it's some other...thing....person...whatever. Wow. I guess John Locke died as he lived -- a gullible fool with no life purpose. And so can we assume that Not!Locke is the entity that's been dwelling in the cabin? The circle of ash was meant to keep him/it trapped inside.
YES!! Locke unknowingly let the bad guy out!!!
So if Miles is right, and Jack was indeed the cause of the incident, then does that mean the incident happened like it always did, and the crash will happen anyway? I mean, we got to see how Chang lost his arm, which we already knew he did. Maybe they piled all that concrete on top of the mess, built the hatch anyway, then spent the next 30 years pushing the button after all.

I spent the whole episode thinking Jacob and the other guy were some kind of Heaven/Hell, Angel/Demon, Jesus/Satan kind of thing, but with Jacob being killed .....So all this build up with Jacob and now he's dead? Outsmarted by Titus Welliver disguised as Locke? So the whole show has been Jacob and his friend, the smoke monster, having an eternal feud. Wow. Was smokey angry about Jacob bringing someone to their island paradise, hence looking for the loophole to kill him? Kind of a let down. Speaking of letdowns, Ben sure turned into a whiny little bitch.
And no way is Juliet dead. She set off the bomb and everyone's going to get sent back to 2007, and everyone will join forces against Evil John Locke.
Goddamn it Miles. We are blowing up a bomb to change the future. This is no time to be thinking out plans or considering the consequence of our actions! Its time to just change in and, while we're at it, discuss how screwed up our love lives are! And how the boys want Kate.
I wonder if Aaron will be the vehicle through which Jacob can reincarnate. Maybe that will somehow fulfill the "he can't be raised by another" prophecy. Maybe Aaron will save them all somehow.
So black shirt guy was a shapeshifter or something like that. He learned a way to take on the body of a dead person (Christian, Locke, Ben's daughter) as a way to get his plan in motion to finally kill Jacob. Can't wait to find out why he wanted Jacob dead (power hungry, jealously?) and what happens now that Jacob is dead.
Interesting that Jacob's death coincided with the 1977 Incident. Maybe the explosion causes time shifts again and they get thrown to 2007!!! That's why he said they are coming!